The Stovebolt Site Forums The Shop Area The Electrical Bay Tach won't settle down

I posted this once before but it was suggested I Post again. I got a nice tach from gauge guys. Its a 6 volt 6 cylinder for my 1954 3100. The first one wouldn't settle down it flop all around it would settle down about halfway through the gears and gradully climb as it should but shift gears and it flops around again. I sent it back to Gauge guys and they replce it with a new version when i got that back this one was worse. I have no problem sending it back but it's a nice tach I pperfer it to work right Any ideas it must be something to do with the signal i'm getting even stuart can't figure it out Has anyone else had this problem .... Thanks Peter

I remember the old thread. You've checked everything that we'd thrown out, and it still does it... Hrm...

I got nothing, except check your voltages and make sure that your grounds and dizzy hookups are good.

Sorry.

Check the dwell.
If the dwell is erratic the tach will jump all over the place. I'm not driving anything with points at the moment. I've had cars that the tach would tell me when the points needed adjusted or replaced, just by the way it acted.
When you rev the engine up, the dwell should not change more than two degrees. Check it with and without the vacuum advance. You could even put the dwell meter next to the tach while you drive it.

Well My problem is I don't know what Dwell means I'm sorry. I think its something to do with the timing..... Peter

Peter,

The point setting can be measured two different ways. One uses a gap gauge and sets the distance between the two little faces in thousandths of an inch.

The other method uses a meter..a dwell meter, to electronically measure the number of degrees the distributor rotor rotates while the points are closed. This value is given in degrees.

While the points are closed, the coil is 'saturating', or sort of filling up with electricity, getting ready to dump all that power across the spark plug gap when the points open...BAM!!

Tune up specs for engines usually include both a point gap and a dwell angle so you could set the points with either a gap gauge or a dwell meter.

I don't know what the dwell on one of these old engines would be.

Remember the Chevy V-8's with the little trap door on the distributor cap. You could pop your Allen wrench into the screw and adjust the dwell as the engine ran....very cool and accurate!

So dwell is the number of degrees of rotation of the distributor rotor that the points stay closed...just a high-tech way of gapping your points.

Do you have any friend or neighbor that has a 6 volt six cylinder engine you could hook your tach up to and verify whether the unit is goofy, or your truck has a problem.

They actually wrote a children's song about this subject...The Farmer In The Dwell!!

Stuart

The points on a 216 should be 18 thousandths if they are new, and 20 thousandths if they've been used... So sayeth the Shop Manual.

I can't imagine that the 235 would be much different.

Petmill,which transmitter are you using??

Have you tryed adjusting the transmitter by removing the transmitter cover and turning the adjusting screw?

You will want to make small adjustments until the needle settles down. Normally needle flutter requires the screw be turned in but you can tell when you make the first small adjustment by watching the needle's reaction.

The key is small adjustments,just read your warranty to see if it allows for adjustments.

Hope this helps.Hobert

A bad distributor shaft bearing can cause the shaft to 'wobble' and make the point setting and dwell eratic which could cause the tach to read erratic.

Another possibility is a freyed tach drive cable.